首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   443717篇
  免费   49720篇
  国内免费   178篇
  2018年   4126篇
  2016年   5613篇
  2015年   7472篇
  2014年   8762篇
  2013年   12086篇
  2012年   13743篇
  2011年   14204篇
  2010年   9825篇
  2009年   9009篇
  2008年   12861篇
  2007年   13370篇
  2006年   12559篇
  2005年   12021篇
  2004年   12122篇
  2003年   11382篇
  2002年   11155篇
  2001年   17934篇
  2000年   17931篇
  1999年   14404篇
  1998年   5299篇
  1997年   5558篇
  1996年   5188篇
  1995年   4867篇
  1994年   4692篇
  1993年   4764篇
  1992年   12054篇
  1991年   11903篇
  1990年   11681篇
  1989年   11305篇
  1988年   10806篇
  1987年   10421篇
  1986年   9654篇
  1985年   9523篇
  1984年   8071篇
  1983年   6959篇
  1982年   5386篇
  1981年   4836篇
  1980年   4660篇
  1979年   7693篇
  1978年   6086篇
  1977年   5624篇
  1976年   5363篇
  1975年   5794篇
  1974年   6500篇
  1973年   6336篇
  1972年   5886篇
  1971年   5374篇
  1970年   4733篇
  1969年   4684篇
  1968年   4495篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
The case of a 53 years old woman was described in whom a congenital factor XIII deficiency was suspected because of deforming scars and hemorrhagic diathesis. A thromboelastographic declination of elasticity as well as decreased factor XIII level up to 5% of normal range were only found in all hemostatic examinations. In 2 children factor XIII decreased to half of its normal level, whereas in the youngest daughter that level was 25%. Sporadically the girl had mild diathesis. No changes in thromboelastograms were observed in members of the patient's family. The platelet function was unchanged in all examined cases.  相似文献   
983.
The isoelectric point of the camel and the human β-endorphin, of the α-endorphin and the enkephalins were determined by analytical isoelectric focusing on 1 mm thin polyacrylamide gel slab. The difficulty of staining peptides as short as β-endorphin or smaller was overcomed using a modification of Bibring and Baxandall's or Faupel and Von Arx's staining method. The camel β-endorphin gives two bands having isoelectric point of 10.3 and 10.4, the human β-endorphin focus at pH 9.9, while α-endorphin, leu and met-enkephalin at pH 5.9, 5.5 and 5.45 respectively. The staining method described coupled with the isoelectric focusing seems to be fit for discriminating β-endorphin in a crude rat pituitary extract.  相似文献   
984.
The influence of surfactant depletion on clearance from the lungs of inhaled technetium-99m-labeled diethylenetriamine pentaacetate (99mTc-DTPA) was studied in rabbits. Surfactant was removed by repeated lung lavage with isotone saline. To minimize structural damage to the lungs, pressure generated insufflation with short expiration was utilized. Aerosolized 99mTc-DTPA was administered via a bag-in-bottle system. Radioactivity was measured with a gamma camera and time-activity curves were obtained over the base of the right lung. Six nonlavaged rabbits served as controls. In six lavaged rabbits clearance of 99mTc-DTPA was significantly faster than in controls. In three rabbits given natural surfactant into the trachea after lung lavage, 99mTc-DTPA was eliminated faster than in controls but slower than in surfactant-depleted animals. The results indicate a role of surfactant on clearance rate of 99mTc-DTPA from rabbit lungs. Measurements of 99mTc-DTPA clearance may be useful in studying the function of the surfactant system in different lung disorders.  相似文献   
985.
986.
987.
988.
False Images     
  相似文献   
989.
Monocytes/macrophages play a critical role in the initiation and progression of a variety of glomerulonephritides. We sought to define the interactions between physiologically activated human monocytes and glomerular mesangial cells (MC) by employing a cell culture system that permits the accurate assessment of the contribution of soluble factors and cell-to-cell contact. Human peripheral blood monocytes, primed with IFN-gamma and GM-CSF, were activated with CD40 ligand (CD40L) or TNF-alpha and cocultured with MC. CD40L-activated monocytes induced higher levels of IL-6, monocyte chemoattractant protein-1 (MCP-1) and ICAM-1 synthesis by MC. Separation of CD40L-activated monocytes from MC by a porous membrane decreased the mesangial synthesis of IL-6 by 80% and ICAM-1 by 45%, but had no effect on MCP-1. Neutralizing Abs against the beta 2 integrins, LFA-1 and Mac-1, decreased IL-6 production by 40 and 50%, respectively. Ligation of mesangial surface ICAM-1 directly enhanced IL-6, but not MCP-1, production. Simultaneous neutralization of soluble TNF-alpha and IL-1 beta decreased MCP-1 production by 55% in membrane-separated cocultures of MC/CD40L-activated monocytes. Paraformaldehyde-fixed CD40L-activated monocytes (to preserve membrane integrity but prevent secretory activity), cocultured with MC at various ratios, induced IL-6, MCP-1, and ICAM-1 synthesis by MC. Plasma membrane preparations from activated monocytes also induced mesangial IL-6 and MCP-1 synthesis. The addition of plasma membrane enhanced TNF-alpha-induced mesangial IL-6 production by approximately 4-fold. Together, these data suggest that the CD40/CD40L is essential for optimal effector function of monocytes, that CD40L-activated monocytes stimulate MC through both soluble factors and cell-to-cell contact mediated pathways, and that both pathways are essential for maximum stimulation of MC.  相似文献   
990.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号